1. Field of the Invention
This invention relates to positioning apparatus, and, more particularly, to precision positioning apparatus in which a driving element is rotatably connected to a driven element for the positioning of the driven element.
2. Description of the Prior Art
The rotary positioning of various types of apparatus may be accomplished by various methods, such as the manual positioning by rotating manually an element to be positioned, or a mechanical positioning system may be used. In a mechanical system, some type of mechanical connection, such as through a gearing system, may be used by which an element, a driving element, may be connected to another element, a driven element, through a system of gears for changing the ratio of the angular movement of the driving element with respect to the angular movement of the driven element. With a substantial difference between the diameters of the two elements, there is achieved a substantial degree of control over the precise positioning of the positioning element. This is, of course, directly related to the ratio of the diameters of the two elements. In this case, the result of the connection of the two elements is also a substantial reduction in the speed of the driven element with respect to the speed of the driving element.
There are basically two types of drive systems, direct and indirect. An electric motor may be used to position an apparatus directly, as when the apparatus is secured by direct connection to the rotating armature of an electric motor, or it may be used to position an apparatus indirectly through a mechanical linkage system, such as a gear, or belt, or cable system. An electric motor, a hydraulic motor, or some other appropriate prime motor may be connected to the driving element.
In U.S. Pat. No. 2,516,092, an electric motor is used to drive a drum around which a cable extends. The cable is connected between a driving drum to which the motor is connected and a remote, driven drum. Rotary movement of the driving drum is imparted to the driven drum through a cable system. The apparatus of the '092 patent is used to move a pointer parallel to a scale which includes calibration marks. The scale is fixed, and rotation of the two drums is accordingly indicated by movement of the pointer. The pointer provides a visual indication of the relationship of the driven drum with respect to a fixed reference point.